TEFM variants impair mitochondrial transcription causing childhood-onset neurological disease

Mutations in the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial respiration. Within this group, an increasing number of mutations have been identified in nuclear genes involved in mitochondrial RNA biology. The TEFM gene encodes the mitochondrial transcription elongation factor responsible for enhancing the processivity of mitochondrial RNA polymerase, POLRMT. We report for the first time that TEFM variants are associated with mitochondrial respiratory chain deficiency and a wide range of clinical presentations including mitochondrial myopathy with a treatable neuromuscular transmission defect. Mechanistically, we show muscle and primary fibroblasts from the affected individuals have reduced levels of promoter distal mitochondrial RNA transcripts. Finally, tefm knockdown in zebrafish embryos resulted in neuromuscular junction abnormalities and abnormal mitochondrial function, strengthening the genotype-phenotype correlation. Our study highlights that TEFM regulates mitochondrial transcription elongation and its defect results in variable, tissue-specific neurological and neuromuscular symptoms.


March 2021
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Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A description of any restrictions on data availability -For clinical datasets or third party data, please ensure that the statement adheres to our policy Field-specific reporting Please select the one below that is the best fit for your research. If you are not sure, read the appropriate sections before making your selection. The authors declare that the data supporting the findings of this study are available within the paper and its supplementary information files. Accession number for TEFM cDNA used in the study is NM_024683.4. The structure of TEFM (PDB ID: 5OLA) was sourced from PDB (https://www.rcsb.org). Diagnostic next generation sequencing data can be made available by the authors on request. Data will be deposited in advance of publication and accession codes from the respective databases will be provided. All data is available with this submission, apart from proprietary scripts. Note that full information on the approval of the study protocol must also be provided in the manuscript.

Human research participants
Policy information about studies involving human research participants Population characteristics
All antibodies listed above were used according to the manufacturer`s recommendation and were validated in control cells and control zebrafish.
Primary skin fibroblasts of patients 2,3,4, and 6 were analyzed in this study. All patients gave informed consent for the use of their cells in this study (see below at human participants and ethics).
None of the cell lines were authenticated in this study.
All cell lines used in this paper were tested negative for Mycoplasma.
No commonly misidentified lines were used.
Zebrafish (AB, Casper and TLF strains), age <5 days post fertilization No field collected samples were used in the study.
No field collected samples were used in the study.
All zebrafish experiments carried out in Canada were performed in accordance with guidelines from the Canadian Council on Animal Care and were approved by the University of Ottawa Animal Care Committee. All zebrafish experiments performed in the UK were carried out in accordance with UK Home Office Guidelines, UK Animals (Scientific Procedures) Act 1986. Adult UK zebrafish were maintained under project licence P1CG6E735.
The patients were of different ethnic background. Patients presented with a history of childhood-onset muscle weakness and/or developmental delay and underwent detailed clinical examination. DNA, tissues including muscle and skin fibroblasts, and medical records were obtained based on standard procedures. Patients 1 and 2 were first identified in RD-Connect GPAP (Genome-Phenome Analysis Platform 36, Patients 3-5 were identified through GeneMatcher, while patients 6 and 7 were matched within the RD-Connect Genome-Phenome Analysis Platform (GPAP).